? ? Prop for Mercruiser 165 at 5k Elevation

[ianboat]

This is the same as a thread I started a little while ago - re-posting to update it:
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We need advice because we're running in lakes at 4,000' to 6,000' elevation (including Lake Tahoe). Seems to be jetted fine for this elevation (runs fine), but we need more power (more torque, better acceleration) , for getting a single-skier up.

Engine: 1972 Mercruiser 165 hp in-line 6
Boat: 1972 SeaRay 19' (SRV 190) - 6 seats - closed bow

WOT is 3400 on a cool (65 F), choppy day - AT 5000' ELEVATION
(didn't get the speed at 3400 - speedometer is broken)

This is with about 800 lbs of passengers in the boat.

WOT SHOULD BE 3900 - 4300

Current prop is - 14.5 x 17 -- 3 blade aluminum

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Mercruiser recommendation for 17'-19' boat is 15 x 23 - 3 blade aluminum
Mercruiser recommendation for 19'-21' boat is 15 1/4 x 21 - 3 blade aluminum.

Our boat is 19', so we're kind of in the middle.

We need to adjust for elevation, but I haven't figured out how that works.

We've never fiddled with a prop before, so don't really have any experience in making changes.

Any recommendations/ explanations would be much appreciated!!!!!!

p.s. we also have a SS Stilletto 14.25 x 17 -- it's dinged and could be fixed --IF it would be worth it -- i.e. if it would give us more power.

 

[junior1113]

Re: ? ? Prop for Mercruiser 165 at 5k Elevation

from the #'s u give you would need to go to 3x15 or 4x14 to get up 400-500 rpms and improve torque. i think there may be other issues in that motor it should be 17-19 based on hp and weight. do comp test an tune up before buying prop. would also check tach

 

[ianboat]

Re: ? ? Prop for Mercruiser 165 at 5k Elevation

Thanks for the feedback.

Let me see if I'm reading you correctly:

"from the #'s u give you would need to go to 3x15 or 4x14 to get up 400-500 rpms and improve torque. i think there may be other issues in that motor it should be 17-19 based on hp and weight. do comp test an tune up before buying prop. would also check tach"

We should go with:
a 3-blade 15" (keep 17" pitch? go with Mercruiser rec for 23" pitch?)
or
a 4-blade 14" (keep 17" pitch? go with Mercruiser rec for 23" pitch?)

We should be looking at Mercruiser's recommendations for the 17'-19' boat.

Did I get that right?

 

[junior1113]

Re: ? ? Prop for Mercruiser 165 at 5k Elevation

u need either a 3x15pitch or a 4x14pitch to get to recomended wot rpm. seems like motor is weak. if you put a 23 pitch on it youd be 3000 wot rpms with no power.

what im saying is if that was a good running 165 it should be able to turn a 19 @4400. unless tach is off of coarse.

whats your wot rpm @ lower elevations. should'nt make that much difference